Method of preparing organosilanes



Patented June 15, 1954 2,681,355 METHOD or PREPARING ORGANOSILANES Arthur J. Barry and John W. Gilkey, Midland, Mich., assignors to Dow Corning Corporation,

Midland, Mich., a corporation of Michigan No Drawing. Application February 20, 1953,

Serial No. 338,123

3 Claims.

This invention relates to the manufacture of methylchlorosilanes.

The primary commercial method for preparing methylchlorosilanes such as CHaSlCla, CH3HSlC12, and (CHahSiCh is that of reacting CHsCl with silicon. This method is known in the art as the direct process and is well described in the patent literature, for example, in U. S. Patents 2,380,995 and 2,488,487. In addition to the above methylchlorosilanes, there is always obtained a liquid material boiling above (CH3)2S1C12 (i. e., above 70 C.) This liquid high boiling product is hereafter referred to as the residue. The residue amounts to about per cent of the total reaction product and is a complex mixture of compounds containing SiSi, SiCSi, and SiOSi linkages in the molecules. The residue is more fully described infra.

Methylchlorosilanes are the raw materials for a major portion of the silicone products now being manufactured. Therefore, the demand for methylchlorosilanes is high. On the other hand, there is to date, little commercial use for the residue. Consequently, large inventories of the residue have been built up by the silicone industry. This inventory poses a serious problem for it represents an expensive, relatively useless material. Furthermore, continued accumulation of the residue poses a storage problem.

It is known from U. S. Patent 2,598,435 that some components of the residue, namely those containing SiSi linkages such as CI-IsClzSiSiClzCHs may be cracked by heat to give methylchloro silanes. According to this patent; the SiSi compounds are separated from the residue before they are cracked. When the process of this patent is applied to the total residue, extensive coking (formation of carbonaceous materials) takes place. For example, it has been found that if the residue is passedthrough a hot tube (heated, say, to 200-900 CL), sufiicient. coking takes place within an hour or so to render the tube unsuitable for further use. Thus, the process is not suitable for commercial cracking of the residue. The process of this invention obviates this coking.

.It is the primary object of this invention to provide a commercially feasible, methodfor ,con; verting a relatively useless material into more highly useful methylchlorosilanesl Another object is to solve the residue problem which is inherent to the production of methylchlorosilanes by the direct process.

In accordance with this invention, the residue boiling above (CH3)2SiCl2, which residue was formed during the reaction of CI-IsCl with silicon, is heated in contact with HCl at a temperature of from 200 C. to 900 C. The HCl is present in amount of at least 4 percent by weight based onthe weight of the residue. This process results in cracking of the residue to give methylchlorosilanes.

The process of the invention begins at once upon heating the mixed HCl and residue. Excellent yields of methylchlorosilanes are obtained at any pressure. It has been found that the reaction proceeds equally well at atmospheric pressure and at pressures upwards of 1500 p. s. i. In general at the lower pressures, higher temperatures are preferred. Thus, atmospheric pressure reactions are preferably carried out at from 400 C. to 900 C. while superatmospheric reactions are preferably carried out at from 200 C. to

The process of this invention lends itself to either batchwise or continuous modes of operation. For example, the residue and H01 may be added to a bomb and heated to reaction temperatures, or the residue and H01 may be passed continously through a heated tube. The latter method is particularly feasible since it has been found that the residue and HCl may be passed continuously through a hot tube for periods in excess of 24 hours without any reduction of the rate of reaction. In other words, the amount of desired products obtained during the 24th hour of operation is the same as during the 1st or 6th hours of operation. A further advantage of the tube procedure is that the unreacted HCl and residue may be recycled through the reactor.

In carrying out the present process at atmospheric pressure in tubes, the tubes may or may not contain packing. If packing is employed, it may be either of inert materials such as quartz or the packing may beof a catalytic type such as activated alumina or silica alumina. In both cases, satisfactory yields of the desired methylchlorosilanes are obtained. In the tube process,

the residue and H01 may be fed separately into 2 G11 the reactor or they may be mixed prior to passage into the reactor.

There should be at least 4 per cent by weight I-ICl based on the weight of the residue, in order for the benefits of the invention to be realized. Larger amounts of HCl may be used, if desired, although no particular advantage is obtained by employing mixtures containing more than per cent by weight 1101. Pure I-ICl gas or HCl gas diluted with other inert gases such as nitro gen or CO2 may be used. The HCl may be recovered from the eiiiuent material and reused if desired.

As previously pointed out, if I-ICl is not employed, the cracking process is characterized by so much coking thatcontinuous operation in a heated tube is impossible. Although it has not been ascertained that the coking phenomena is solely responsible for low yields of (CH3)3SiC12 and CI-IsSiCls, it is a fact that much lower yields of these silanes are obtained if HCl is not employed irrespective of whether the reaction is carried out in a sealed bomb at superatmospheric pressure or in a tube at atmospheric pressure.

The residue employed herein consists of a very complex mixture of a large number of silanes, disilanes, disiloxanes, silmethylene compounds, and silethylene and other polymeric compounds. Table I, whichfollows, lists the products identifled in the residue of a representative industrial scale reaction of CHsCl and Si. The boiling points listed are in degrees centigrade at atmospheric pressure.

TABLE I Compound: B. P., C. Ethyltrichlorosilane Ethylmethyldichlorosilane 102 Isopropyltrichlorosilane i 118 Isopropylmethyldichlorosilane 119 n-Propyltrichlorosilane 124 n-Propylmethyldichlorosilane 125 Hexachlorodisiloxane 136 CH3C12SiOSiC13 140 Isobutyltrichlorosilane 141.5 Hexachlorodisilane 146 (CH3)2ClSi-SiCl3 157 CH3C12S1OS1C12CH3 158 (CF13) 2ClSiCH2SiCl CH3 2 178 (CH3)2ClSiCI-I2SiCl3 ClzSiCl-IcSlCls 185 ClsSiCI-IzSiClzCI-Is 189 CHsClaSiCHaSlClzCI-Is 192 CBHtSiClz 201 CHLaClzSiCI-IzCI-IzSiCla 206 It can be seen that the residue is composed primarily of compounds which have methyl and/or higher alkyl radicals attached to silicon. When HCl is reacted with these compounds at the temperatures of this invention, the SiSi, 5108i and SiCSi linkages are split to produce meth'ylchlorosilanes having only one silicon atom terial boiling quantitative distillation of the residue is possible. This is due to the fact that a first distillation of the residue gives a distillate of gradually increasing boiling point. Repeated fractionations of selected portions ultimate y yield pure compounds; however, the identity of mabetween the identified compounds has not been ascertained. Due to varying reaction conditions such as temperature, feed rate, and catalysts employed in the direct process. the composition of the residue varies somewhat with respect to ratio of organic groups per silicon. The residue generally has a hydrolyzable chlorine to Si atomic ratio ranging from 1.4:1 to 2.311, a monovalent hydrocarbon to Si (R/Si) ratio ranging from 1.0 to 1.5. This variation of chlorine and hydrocarbon content does not aifect the operability of the residue in the present invention.

The silanes produced by the practice of this invention are all highly utilizable materials which may be employed for preparing other organosilicon materials such as resins, fluids, etc., or they may be used directly in water-repellent 1 treatment of organic and inorganic materials.

This invention is illustrated by the following examples. However, the scope thereof is limited only as set forth in the claims.

Example 1 The residue employed in this example has the following approximate composition as determined by a distillation analysis.

Men SiCI-IzSi) C16n MenSiCH2CH2Si(C1s-n) MeMSiCHzSiCHeSi) 018-11.

4.1 per cent residue which comprised higher polymeric siloxanes, silanes, and silcarbanes of the above types.

In each case above, 11 has a value from 1 to 3.

of the formula This example illustrates vapor phase cleavage of the residue at atmospheric pressure. In each of the runs shown in Table II below, the residue and HCl were fed simultaneously and separately into a four foot stainless steel tube having an inside diameter of one inch. The tube was maintained at the temperatures indicated in the table, and the materials were passed through for the indicated time. .In each run the efliuent material was collected in a water cooled condenser and in a dry ice trap. The condensates were combined in each run and were fractionally distilled up to a head temperature of 75 C. In each case, the material boiling between 35 C. and 75 C. was

analyzed by infra red and found to consist essen-.

tially of the silanes listed in the table. 'All per cents by weight shown in the table are based upon the total weight of the residue and HCl passed through the tube. In each run, the HCl was employed in amount of about 1 mol of HCl per 185 g. of the residue.

TABLE II T i qi i Tim M P t P t P t P t emp., ee ee ercen ercen ercen ercen Tube Packmg O 0. Rate, Rate, flg g SiOh Messiah MezSiClz MeSiOh cc./min. ccJmin. 1

1 Quartz 700 2.00 300 4. 5 4. 2 2. a 13. 5 20.2 2 -.d 750 2. 12 300 6. O 4. trace 18. 1 25. 6 3 Silica-alumina 500 2. 77 300 4. 3 5. 3 2. l 9. 2 23. 8 4. 600 2. 300 3. 5 5. 4 l. 8 8. 2 29. 5 5. 450 2. 10 300 2. 9. 6 trace 5. 1 21. 2 6. 500 2. 10 300 4. 75 13. 5 trace 9. 2 39. 5 7 700 4. 500 3. 25 8. 9 0. 8 10. 3 28. 8

In each of the above runs, the tube was examined after 5 hours, and it was found that there was negligible coking.

Example 2 15 2. A method of preparing methylchlorosilanes Table III which follows shows that excellent which comprises reacting a mixture of the resi yields f methylchlomsflanes are obtained in a due boiling above dimethyldichlorosilane, which batchwise process employing superatmospheric resume was formed during the reaction of methylpressure. In each run shown in the table, the chlorlde d silicon, and H01 at atm sphe i process was carried out as follows: A 2.4 liter p su at a temperature o om 4 C- to steel bomb was charged with the indicated 900 0., the HCl being present in amount of at amount of the residue employed in Example 1 least 4 per cent by weight based on the weight and H01 gas and then heated to the indicated of th idu t a u The Q commuously 3. A method of preparing methylchlorosilanes ti g the 33 g g- At the i f which comprises reacting the residue boiling g gi gg gfii f g gi zg above dimethyldichlorosilane, which residue was the reaction product was fractionally distilled to fqrmet} durmg the react-Ion of methylihlmde remove an of the products boiling below 9 w1th silicon, and HCl at superatmospheric presto give the silanes listed in the table. All persure at a tmpelature m centages in Table III are expressed as per cent the HCl bemg Present m amount at least 4 by weight based on the total weight of reaction P n y welght based on the weight of the product. residue.

TABLE III weight Weight Temp, Pressure, Time, Re t ion Percent Percent Percent Percent Run Residue H01.,g. 0. p. s. 1. Hours Product s10]. MeHSiOh MezSiCh MeSiOl;

a ing.

1 600 97 342-354 1, 3501,390 16 620 5.5 1.8 11.3 43.4 2 s00 97 390-400 1, 600-1, 640 is 610 11.8 1.8 11.3 38.7 s e00 132 295-310 1,350 1,575 16 550 5.9 2.0 7.3 35.5 4 s00 97 395F409 1,425 2 605 9.5 0.9 4.2 31

That which is claimed is:

1. A method of preparing methylchlorosilanes which comprises heating the residue boiling above dimethyldichlorosilane, which residue was formed during the reaction of methylchloride 2, 8, with silicon, and H01 at a temperature of from 62 243 200 C. to 900 C., the H01 being present in amount of at least 4 per cent by weight based on the weight of the residue.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,598,435 Mohler May 27, 1952 Barry Feb. 10, 1953 FOREIGN PATENTS Number Country Date 666,512 Great Britain Feb. 13, 1952 

1. A METHOD OF PREPARING METHYLCHLOROSILANES WHICH COMPRISES HEATING THE RESIDUE BOILING ABOVE DIEMTHYLDICHLOROSILANE, WHICH RESIDUE WAS FORMED DURING THE REACTION OF METHYLCHLORIDE WITH SILICON, AND HCI AT A TEMPERATURE OF FROM 200* C. TO 900* C., THE HCI BEING PRESENT IN AMOUNT OF AT LEAST 4 PER CENT BY WEIGHT BASED ON THE WEIGHT OF THE RESIDUE. 